336 mg (1.05 mmol) of TBTU, 161 mg (1.05 mmol) of HOBt, 1.02 mL triethylamine and 326 mg (1.05 mmol) of 1-(1-methyl-piperidin-4-yl)-piperazine (used as the tris-hydrochloride) were added to a solution of 500 mg (1.05 mmol) of 3-(3,4-diethyl-phenyl)-2-{[4-(2-oxo-1,4-dihydro-2H-quinazolin-3-yl)-piperidine-1-carbonyl]-amino}-propionic acid in 100 mL of THF, stirred for 4 h at RT and 2 h at 40° C. The solvent was removed in vacuo, the residue was stirred with 40 mL of saturated NaHCO3 solution, the precipitated product was suction filtered, taken up in MeOH and purified by chromatography over silica gel (MeOH). The product fractions were evaporated down, the residue triturated with diethyl ether, suction filtered, washed twice with diethyl ether and dried.
